| 1 | /* |
| 2 | * Copyright 2006-2007 the original author or authors. |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | package org.springframework.batch.repeat.support; |
| 18 | |
| 19 | import java.util.ArrayList; |
| 20 | import java.util.Arrays; |
| 21 | import java.util.Collection; |
| 22 | import java.util.List; |
| 23 | |
| 24 | import org.apache.commons.logging.Log; |
| 25 | import org.apache.commons.logging.LogFactory; |
| 26 | import org.springframework.batch.repeat.CompletionPolicy; |
| 27 | import org.springframework.batch.repeat.ExitStatus; |
| 28 | import org.springframework.batch.repeat.RepeatCallback; |
| 29 | import org.springframework.batch.repeat.RepeatContext; |
| 30 | import org.springframework.batch.repeat.RepeatException; |
| 31 | import org.springframework.batch.repeat.RepeatListener; |
| 32 | import org.springframework.batch.repeat.RepeatOperations; |
| 33 | import org.springframework.batch.repeat.exception.DefaultExceptionHandler; |
| 34 | import org.springframework.batch.repeat.exception.ExceptionHandler; |
| 35 | import org.springframework.batch.repeat.policy.DefaultResultCompletionPolicy; |
| 36 | import org.springframework.util.Assert; |
| 37 | |
| 38 | /** |
| 39 | * Simple implementation and base class for batch templates implementing |
| 40 | * {@link RepeatOperations}. Provides a framework including interceptors and |
| 41 | * policies. Subclasses just need to provide a method that gets the next result |
| 42 | * and one that waits for all the results to be returned from concurrent |
| 43 | * processes or threads.<br/> |
| 44 | * |
| 45 | * N.B. the template accumulates thrown exceptions during the iteration, and |
| 46 | * they are all processed together when the main loop ends (i.e. finished |
| 47 | * processing the items). Clients that do not want to stop execution when an |
| 48 | * exception is thrown can use a specific {@link CompletionPolicy} that does not |
| 49 | * finish when exceptions are received. This is not the default behaviour.<br/> |
| 50 | * |
| 51 | * Clients that want to take some business action when an exception is thrown by |
| 52 | * the {@link RepeatCallback} can consider using a custom {@link RepeatListener} |
| 53 | * instead of trying to customise the {@link CompletionPolicy}. This is |
| 54 | * generally a friendlier interface to implement, and the |
| 55 | * {@link RepeatListener#after(RepeatContext, ExitStatus)} method is passed in |
| 56 | * the result of the callback, which would be an instance of {@link Throwable} |
| 57 | * if the business processing had thrown an exception. If the exception is not |
| 58 | * to be propagated to the caller, then a non-default {@link CompletionPolicy} |
| 59 | * needs to be provided as well, but that could be off the shelf, with the |
| 60 | * business action implemented only in the interceptor. |
| 61 | * |
| 62 | * @author Dave Syer |
| 63 | * |
| 64 | */ |
| 65 | public class RepeatTemplate implements RepeatOperations { |
| 66 | |
| 67 | protected Log logger = LogFactory.getLog(getClass()); |
| 68 | |
| 69 | private RepeatListener[] listeners = new RepeatListener[] {}; |
| 70 | |
| 71 | private CompletionPolicy completionPolicy = new DefaultResultCompletionPolicy(); |
| 72 | |
| 73 | private ExceptionHandler exceptionHandler = new DefaultExceptionHandler(); |
| 74 | |
| 75 | /** |
| 76 | * Set the listeners for this template, registering them for callbacks at |
| 77 | * appropriate times in the iteration. |
| 78 | * |
| 79 | * @param listeners |
| 80 | */ |
| 81 | public void setListeners(RepeatListener[] listeners) { |
| 82 | this.listeners = listeners; |
| 83 | } |
| 84 | |
| 85 | /** |
| 86 | * Register an additional listener. |
| 87 | * |
| 88 | * @param listener |
| 89 | */ |
| 90 | public void registerListener(RepeatListener listener) { |
| 91 | List list = new ArrayList(Arrays.asList(listeners)); |
| 92 | list.add(listener); |
| 93 | listeners = (RepeatListener[]) list.toArray(new RepeatListener[list.size()]); |
| 94 | } |
| 95 | |
| 96 | /** |
| 97 | * Setter for exception handler strategy. The exception handler is called at |
| 98 | * the end of a batch, after the {@link CompletionPolicy} has determined |
| 99 | * that the batch is complete. By default all exceptions are re-thrown. |
| 100 | * |
| 101 | * @see ExceptionHandler |
| 102 | * @see DefaultExceptionHandler |
| 103 | * @see #setCompletionPolicy(CompletionPolicy) |
| 104 | * |
| 105 | * @param exceptionHandler the {@link ExceptionHandler} to use. |
| 106 | */ |
| 107 | public void setExceptionHandler(ExceptionHandler exceptionHandler) { |
| 108 | this.exceptionHandler = exceptionHandler; |
| 109 | } |
| 110 | |
| 111 | /** |
| 112 | * Setter for policy to decide when the batch is complete. The default is to |
| 113 | * complete normally when the callback returns a {@link ExitStatus} which is |
| 114 | * not marked as continuable, and abnormally when the callback throws an |
| 115 | * exception (but the decision to re-throw the exception is deferred to the |
| 116 | * {@link ExceptionHandler}). |
| 117 | * |
| 118 | * @see #setExceptionHandler(ExceptionHandler) |
| 119 | * |
| 120 | * @param terminationPolicy a TerminationPolicy. |
| 121 | * @throws IllegalArgumentException if the argument is null |
| 122 | */ |
| 123 | public void setCompletionPolicy(CompletionPolicy terminationPolicy) { |
| 124 | Assert.notNull(terminationPolicy); |
| 125 | this.completionPolicy = terminationPolicy; |
| 126 | } |
| 127 | |
| 128 | /** |
| 129 | * Execute the batch callback until the completion policy decides that we |
| 130 | * are finished. Wait for the whole batch to finish before returning even if |
| 131 | * the task executor is asynchronous. |
| 132 | * |
| 133 | * @see org.springframework.batch.repeat.RepeatOperations#iterate(org.springframework.batch.repeat.RepeatCallback) |
| 134 | */ |
| 135 | public ExitStatus iterate(RepeatCallback callback) { |
| 136 | |
| 137 | RepeatContext outer = RepeatSynchronizationManager.getContext(); |
| 138 | |
| 139 | ExitStatus result = ExitStatus.CONTINUABLE; |
| 140 | try { |
| 141 | // This works with an asynchronous TaskExecutor: the |
| 142 | // interceptors have to wait for the child processes. |
| 143 | result = executeInternal(callback); |
| 144 | } |
| 145 | finally { |
| 146 | RepeatSynchronizationManager.clear(); |
| 147 | if (outer != null) { |
| 148 | RepeatSynchronizationManager.register(outer); |
| 149 | } |
| 150 | } |
| 151 | |
| 152 | return result; |
| 153 | } |
| 154 | |
| 155 | /** |
| 156 | * Internal convenience method to loop over interceptors and batch |
| 157 | * callbacks. |
| 158 | * |
| 159 | * @param callback the callback to process each element of the loop. |
| 160 | * |
| 161 | * @return the aggregate of {@link ContinuationPolicy#canContinue(Object)} |
| 162 | * for all the results from the callback. |
| 163 | * |
| 164 | */ |
| 165 | private ExitStatus executeInternal(final RepeatCallback callback) { |
| 166 | |
| 167 | // Reset the termination policy if there is one... |
| 168 | RepeatContext context = start(); |
| 169 | |
| 170 | // Make sure if we are already marked complete before we start then no |
| 171 | // processing takes place. |
| 172 | boolean running = !isMarkedComplete(context); |
| 173 | |
| 174 | for (int i = 0; i < listeners.length; i++) { |
| 175 | RepeatListener interceptor = listeners[i]; |
| 176 | interceptor.open(context); |
| 177 | running = running && !isMarkedComplete(context); |
| 178 | if (!running) |
| 179 | break; |
| 180 | } |
| 181 | |
| 182 | // Return value, default is to allow continued processing. |
| 183 | ExitStatus result = ExitStatus.CONTINUABLE; |
| 184 | |
| 185 | RepeatInternalState state = createInternalState(context); |
| 186 | Collection throwables = state.getThrowables(); |
| 187 | |
| 188 | try { |
| 189 | |
| 190 | while (running) { |
| 191 | |
| 192 | /* |
| 193 | * Run the before interceptors here, not in the task executor so |
| 194 | * that they all happen in the same thread - it's easier for |
| 195 | * tracking batch status, amongst other things. |
| 196 | */ |
| 197 | for (int i = 0; i < listeners.length; i++) { |
| 198 | RepeatListener interceptor = listeners[i]; |
| 199 | interceptor.before(context); |
| 200 | // Allow before interceptors to veto the batch by setting |
| 201 | // flag. |
| 202 | running = running && !isMarkedComplete(context); |
| 203 | } |
| 204 | |
| 205 | // Check that we are still running... |
| 206 | if (running) { |
| 207 | |
| 208 | logger.debug("Batch operation about to start at count=" + context.getStartedCount()); |
| 209 | |
| 210 | try { |
| 211 | |
| 212 | result = getNextResult(context, callback, state); |
| 213 | executeAfterInterceptors(context, result); |
| 214 | |
| 215 | } |
| 216 | catch (Throwable throwable) { |
| 217 | |
| 218 | // An exception alone is not sufficient grounds for not |
| 219 | // continuing |
| 220 | Throwable unwrappedThrowable = unwrapIfRethrown(throwable); |
| 221 | try { |
| 222 | |
| 223 | for (int i = listeners.length; i-- > 0;) { |
| 224 | RepeatListener interceptor = listeners[i]; |
| 225 | interceptor.onError(context, unwrappedThrowable); |
| 226 | // This is not an error - only log at debug |
| 227 | // level. |
| 228 | logger.debug("Exception intercepted (" + (i + 1) + " of " + listeners.length + ")", |
| 229 | unwrappedThrowable); |
| 230 | } |
| 231 | |
| 232 | exceptionHandler.handleException(context, unwrappedThrowable); |
| 233 | |
| 234 | } |
| 235 | catch (Throwable handled) { |
| 236 | throwables.add(handled); |
| 237 | } |
| 238 | } |
| 239 | |
| 240 | // N.B. the order may be important here: |
| 241 | if (isComplete(context, result) || isMarkedComplete(context) || !throwables.isEmpty()) { |
| 242 | running = false; |
| 243 | } |
| 244 | } |
| 245 | |
| 246 | } |
| 247 | |
| 248 | result = result.and(waitForResults(state)); |
| 249 | |
| 250 | // Explicitly drop any references to internal state... |
| 251 | state = null; |
| 252 | |
| 253 | } |
| 254 | /* |
| 255 | * No need for explicit catch here - if the business processing threw an |
| 256 | * exception it was already handled by the helper methods. An exception |
| 257 | * here is necessarily fatal. |
| 258 | */ |
| 259 | finally { |
| 260 | |
| 261 | try { |
| 262 | |
| 263 | if (!throwables.isEmpty()) { |
| 264 | rethrow((Throwable) throwables.iterator().next()); |
| 265 | } |
| 266 | |
| 267 | } |
| 268 | finally { |
| 269 | |
| 270 | try { |
| 271 | for (int i = listeners.length; i-- > 0;) { |
| 272 | RepeatListener interceptor = listeners[i]; |
| 273 | interceptor.close(context); |
| 274 | } |
| 275 | } |
| 276 | finally { |
| 277 | // TODO: extend this to the completion policy? |
| 278 | context.close(); |
| 279 | } |
| 280 | |
| 281 | } |
| 282 | |
| 283 | } |
| 284 | |
| 285 | return result; |
| 286 | |
| 287 | } |
| 288 | |
| 289 | /** |
| 290 | * Re-throws the original throwable if it is unchecked, wraps checked |
| 291 | * exceptions into {@link RepeatException}. |
| 292 | */ |
| 293 | private static void rethrow(Throwable throwable) throws RuntimeException { |
| 294 | if (throwable instanceof Error) { |
| 295 | throw (Error) throwable; |
| 296 | } |
| 297 | else if (throwable instanceof RuntimeException) { |
| 298 | throw (RuntimeException) throwable; |
| 299 | } |
| 300 | else { |
| 301 | throw new RepeatException("Exception in batch process", throwable); |
| 302 | } |
| 303 | } |
| 304 | |
| 305 | /** |
| 306 | * Unwraps the throwable if it has been wrapped by {@link #rethrow(Throwable)}. |
| 307 | */ |
| 308 | private static Throwable unwrapIfRethrown(Throwable throwable) { |
| 309 | if (throwable instanceof RepeatException) { |
| 310 | return throwable.getCause(); |
| 311 | } |
| 312 | else { |
| 313 | return throwable; |
| 314 | } |
| 315 | } |
| 316 | |
| 317 | /** |
| 318 | * Create an internal state object that is used to store data needed |
| 319 | * internally in the scope of an iteration. Used by subclasses to manage the |
| 320 | * queueing and retrieval of asynchronous results. The default just provides |
| 321 | * an accumulation of Throwable instances for processing at the end of the |
| 322 | * batch. |
| 323 | * |
| 324 | * @param context the current {@link RepeatContext} |
| 325 | * @return a {@link RepeatInternalState} instance. |
| 326 | */ |
| 327 | protected RepeatInternalState createInternalState(RepeatContext context) { |
| 328 | return new RepeatInternalStateSupport(); |
| 329 | } |
| 330 | |
| 331 | /** |
| 332 | * Get the next completed result, possibly executing several callbacks until |
| 333 | * one finally finishes. |
| 334 | * |
| 335 | * @param context current BatchContext. |
| 336 | * @param callback the callback to execute. |
| 337 | * @param state maintained by the implementation. |
| 338 | * @return a finished result. |
| 339 | * |
| 340 | * @see #isComplete(RepeatContext) |
| 341 | */ |
| 342 | protected ExitStatus getNextResult(RepeatContext context, RepeatCallback callback, RepeatInternalState state) |
| 343 | throws Throwable { |
| 344 | try { |
| 345 | update(context); |
| 346 | return callback.doInIteration(context); |
| 347 | } |
| 348 | catch (Throwable t) { |
| 349 | throw t; |
| 350 | } |
| 351 | } |
| 352 | |
| 353 | /** |
| 354 | * If necessary, wait for results to come back from remote or concurrent |
| 355 | * processes. By default does nothing and returns true. |
| 356 | * |
| 357 | * @param state the internal state. |
| 358 | * @return true if {@link #canContinue(ExitStatus)} is true for all results |
| 359 | * retrieved. |
| 360 | */ |
| 361 | protected boolean waitForResults(RepeatInternalState state) { |
| 362 | // no-op by default |
| 363 | return true; |
| 364 | } |
| 365 | |
| 366 | /** |
| 367 | * Check return value from batch operation. |
| 368 | * |
| 369 | * @param value the last callback result. |
| 370 | * @return true if the value is {@link ExitStatus#CONTINUABLE}. |
| 371 | */ |
| 372 | protected final boolean canContinue(ExitStatus value) { |
| 373 | return ((ExitStatus) value).isContinuable(); |
| 374 | } |
| 375 | |
| 376 | private boolean isMarkedComplete(RepeatContext context) { |
| 377 | boolean complete = context.isCompleteOnly(); |
| 378 | if (context.getParent() != null) { |
| 379 | complete = complete || isMarkedComplete(context.getParent()); |
| 380 | } |
| 381 | if (complete) { |
| 382 | logger.debug("Batch is complete according to context alone."); |
| 383 | } |
| 384 | return complete; |
| 385 | |
| 386 | } |
| 387 | |
| 388 | /** |
| 389 | * Convenience method to execute after interceptors on a callback result. |
| 390 | * |
| 391 | * @param context the current batch context. |
| 392 | * @param value the result of the callback to process. |
| 393 | */ |
| 394 | protected void executeAfterInterceptors(final RepeatContext context, ExitStatus value) { |
| 395 | |
| 396 | // Don't re-throw exceptions here: let the exception handler deal with |
| 397 | // that... |
| 398 | |
| 399 | if (value != null && value.isContinuable()) { |
| 400 | for (int i = listeners.length; i-- > 0;) { |
| 401 | RepeatListener interceptor = listeners[i]; |
| 402 | interceptor.after(context, value); |
| 403 | } |
| 404 | |
| 405 | } |
| 406 | |
| 407 | } |
| 408 | |
| 409 | /** |
| 410 | * Delegate to the {@link CompletionPolicy}. |
| 411 | * |
| 412 | * @see org.springframework.batch.repeat.CompletionPolicy#isComplete(RepeatContext, |
| 413 | * ExitStatus) |
| 414 | */ |
| 415 | protected boolean isComplete(RepeatContext context, ExitStatus result) { |
| 416 | boolean complete = completionPolicy.isComplete(context, result); |
| 417 | if (complete) { |
| 418 | logger.debug("Batch is complete according to policy and result value."); |
| 419 | } |
| 420 | return complete; |
| 421 | } |
| 422 | |
| 423 | /** |
| 424 | * Delegate to {@link CompletionPolicy}. |
| 425 | * |
| 426 | * @see org.springframework.batch.repeat.CompletionPolicy#isComplete(RepeatContext) |
| 427 | */ |
| 428 | protected boolean isComplete(RepeatContext context) { |
| 429 | boolean complete = completionPolicy.isComplete(context); |
| 430 | if (complete) { |
| 431 | logger.debug("Batch is complete according to policy alone not including result."); |
| 432 | } |
| 433 | return complete; |
| 434 | } |
| 435 | |
| 436 | /** |
| 437 | * Delegate to the {@link CompletionPolicy}. |
| 438 | * |
| 439 | * @see org.springframework.batch.repeat.CompletionPolicy#start(RepeatContext) |
| 440 | */ |
| 441 | protected RepeatContext start() { |
| 442 | RepeatContext parent = RepeatSynchronizationManager.getContext(); |
| 443 | RepeatContext context = completionPolicy.start(parent); |
| 444 | RepeatSynchronizationManager.register(context); |
| 445 | logger.debug("Starting batch step."); |
| 446 | return context; |
| 447 | } |
| 448 | |
| 449 | /** |
| 450 | * Delegate to the {@link CompletionPolicy}. |
| 451 | * |
| 452 | * @see org.springframework.batch.repeat.CompletionPolicy#update(RepeatContext) |
| 453 | */ |
| 454 | protected void update(RepeatContext context) { |
| 455 | completionPolicy.update(context); |
| 456 | } |
| 457 | |
| 458 | } |